With the increasing of a display size and the frequency of a drive circuit, the migration rate of the conventional amorphous silicon thin film transistors are hard to meet user's requirements.
A thin film transistor (TFT) with a high migration rate comprises a polycrystalline silicon TFT and a metal oxide TFT. In comparison, the polycrystalline silicon TFT has a poor homogeneity and a complex manufacturing process, and it is not good for mass production due to the limitation of laser crystallization equipment; however, the metal oxide TFT has advantages of high migration rate, good homogeneity, transparent and a simple manufacturing process, which can better meet the requirements of large size liquid crystal display (LCD), organic light-emitting-diode display (OLED) and polymer light-emitting-diode display (PLED), therefore, it gets wide attention.
Generally, for a thin film transistor (TFT), a certain energy barrier is produced on an interface surface between a source-drain electrode and a semiconductor active layer so as to form contact resistance; and the energy barrier can hinder the movement of the carrier. When the energy barrier is large at the interface and forms a Schottky contact, it will cause the loss of signal, thereby affect the performance of the TFT.
Furthermore, in the process of manufacturing the conventional metal oxide TFT, when the source-drain metal layer on the MOS active layer are etched in subsequent processes, it is possible to damage the MOS active layer, thereby to reduce the performance of the TFT. Therefore, an etching stop layer is provided over the MOS active layer to prevent the MOS active layer being damaged in the subsequent manufacturing processes. However, the addition of the etching stop layer will increase the complexity of the TFT manufacturing procedure and the cost. Therefore, it is important to simplify the manufacturing process without losing the performance of the TFT.